Grinding machines



Oct. 27, 1964 Filed Dec. 1'7, 1962 F. BIRCH GRINDING MACHINES O 29 I 3/ i 43 32 i 3 3 i 1 4/ 35 L31 -12 37 3a T39 77 i I g i 1 i 34\ i l l/ I l 1 I 5 Sheets-Sheet l lNvEN-rosa FREDEEKZK BIRCH ATTORNEYS Oct. 27, 1964 Filed Dec. 1'7, 1962 F. BIRCH 3,153,883

GRINDING MACHINES 5 Sheets-Sheet 3 INvEN-roQ FREDERICK BIRCH BY 60W fimwamm ATTORNEYS NVENTOR FREDEE\C\ BIRCH A'FFORNEYS Oct. 27, 1964 F. BIRCH GRINDING MACHINES 5 Sheets-Sheet 4 Filed Dec. 17, 1962 Fla. 5.

5 Sheets-Sheet 5 Filed Dec. 17, 1962 FIG] lNvEN-roR FREDEECK E\Q H BY M United States Patent Ofiice 3,153,883 Patented Oct. 2 7, 196% 3,153,883 GRINDING MACHINES Frederick Birch, London, England, assignor to Raphaels Limited, London, England, a company of Great Britain Filed Dec. 17, 1962, Ser. No. 245,015 Claims priority, application Great Britain Dec. 18, 1961 11 Claims. (Cl. 51-169) This invention relates to machines for grinding workpieces such as optical lenses or other optical elements or metallographic specimens. The term grinding is used in a broad sense to include polishing with rouge or similar fine abrasive as well as smoothing with a coarser abrasive such as emery paste. The machines to which the invention relates are of the general kind in which the workpiece is mounted in a holder which is caused to move relatively to a fixed tool having a surface the shape of which is the complement of the desired shape of the surface being ground, the holder being constrained to prevent any rotation of the work-piece about an axis normal to the surface being ground, eg in the case of a cylindrical or toroid lens to prevent rotation of the lens about its optical axis.

It is an object of the invention to provide such a machine which is of simple construction than hitherto which provides the desired irregular movement of the work-piece while preventing rotation of the workpiece about an axis normal to the surface being ground, and which can be so constructed that it is not susceptible to excessive wear even in the abrasive environment in which such machines normally work. It is a further object of the invention to provide an improved means for mounting the work-piece.

According to the present invention, a grinding machine includes a work-piece holder in the form of an arm having mounting means for the work-piece at one end and supported at a point remote from that end in a universal bearing as hereinafter defined, a linkage connecting the arm to a fixed part of the machine and arranged to prevent rotation of the arm but to permit swinging of the arm in all directions transverse to its length, and means for producing such swinging movements of the arm.

By universal bearing is meant a hearing which permits such swinging movements of the arm in any direction transverse to its length, at least up to the maximum amplitude required. Since the amplitude will in any event be relatively small the angular movement of the arm at the hearing will be only a few degrees, and it is sufiicient for the bearing to provide freedom for only such relatively limited angular movement.

It has been found that a simple bush of rubber or similar elastomeric material provides sufiicient freedom of angular movement for the arm, and consequently such a bush may constitute the universal bearing. An advantage of such a bush over other types of universal bearing such as a metal ball and socket joint is that there is no relative sliding or rolling movement which is important in a grinding machine wherein highly abrasive materials are used.

The invention may be performed in various ways and a specific embodiment will now be described by way of example with reference to the accompanying drawings, in which:

FIGURE 1 is a side view of a grinding machine embodying the invention;

FIGURE 2 is a front view of the machine shown in FIGURE 1;

FIGURE 3 is a top plan view of the machine;

FIGURE 4 is an inverted plan view;

FIGURE 5 shows a detail of the work-piece mounting means;

FIGURE 6 is an inverted plan view taken on the lines VIVI in FIGURE 5;

FIGURE 7 is a side view of an alternative form of work-piece mounting means, looking in the direction of the arrow VII in FIGURE 9; i

FIGURE 8 is a front view of the mounting means shown in FIGURE 7; and

FIGURE 9 is an inverted plan view of the mounting means shown in FIGURES 7 and 8.

For convenience, the machine will be described in relation to the grinding of a cylindrical lens, but it is to be understood that the machine can be used for grinding other articles.

The machine shown in FIGURES 1 to 4 comprises a base It to which is fixed an upright tubular post 11. Mounted on the base 11 is an electric motor 12. This motor has a vertical driving shaft 13 which extends into a chamber 14 in the base 10. The driving shaft 13 is fitted with a pulley 15 which by means of a belt 16 drives a larger pulley 17 having fixed thereto a smaller pulley 13 both of which are rotatably mounted on an idler shaft 19. The belt 16 also drives a pulley 20 which is fixed to the bottom of an upright shaft 21 which passes through the interior of the tubular post 11. Before it enters the post 11 the shaft 21 passes through a pump 22 which is located in the base 18. The pump 22, which is of a type known per se, delivers an abrasive medium, i.e. a liquid having abrasive particles suspended therein, via a pipe 23 to which can be connected a flexible rubber tube (not shown) which is disposed to deliver the abrasive medium to the vicinity of the lens being ground and which will be referred to in greater detail below. The front portion 24 of the base 10 is in the form of a basin which collects the abrasive medium and allows it to drain back to the inlet of the pump 22.

Fixed to the top of the post 11 is a head 25 which includes a worm gear casing 26 into which the upper end of the shaft 21 projects. Fixed to the top of the shaft 21 within the casing 26 is a worm (not shown) which engages a worm wheel (not shown) mounted on one end of a shaft 27 so that as the shaft 21 rotates the worm gearing drives the shaft 27 at a lower rotational speed. The head 25 also carries another worm gear casing 28 at its front end. A worm (not shown) on the front end of the shaft 27 engages a worm wheel (not shown) mounted horizontally within the casing 28 on a downwardly projecting tubular shaft 29. Owing to the worm gearing in the casing 28 the tubular shaft 29 rotates more slowly than the shaft 27.

The tubular shaft 29 contains a flexible bush (shown in FIGURE 2 by cutting away a portion of shaft 29 to picture this portion of the structure in cross-section) and within this bush is a rod 31 which, by virtue of the resilience of the bush, can tilt through small angles from the vertical in any direction. Thus, the bush acts as a universal bearing as defined above. Fixed to the rod 31 is a disc 32, and connected to the disc 32 with its axis somewhat offset in relation to the axis of the rod 31 is 'a rod 33. Thus, as the tubular shaft 29 and the rod 31 and the disc 32 slowly rotate about a common vertical axis, the rod 33 is also rotated, its axis performing a circular path the radius of which is equal to the ofiset of this axis in relation to the axis of the rod 31.

Mounted on bushes on the rod 33 so as to be telescopically slidable thereon and to permit the rod to rotate therein is a tube 34 which constitutes the lens holder arm. The tube 34 is prevented from rotation by a linkage connected to a cross-piece 35 fixed to the tube 34. The cross-piece 35 has flexible bushes 37 at its outer ends and fixed to the housing of the bushes 37 are thin, laterally flexible links 38 the rear ends of which are fixed to the housings of further flexible bushes 39. Project- 40 is a yoke member 41 having a circular portion 42 which surrounds the post 1'1'with a clearance, and vertically extending lugs 43 the upper ends of which are fixed to the housings of the bushes 49. 'The yoke member 41 can thus swing from left to right in FIGURE 1 through a few degrees on either side of the vertical. Projecting from the sides of the circular portion 42 of the yoke member 41 are pins 44 (FIGURE 3) which enter the bushes 39. Thus, the linkage comprising the parts 37 to 44 prevents the tube 34 from rotating but permits it to swing in any direction from the vertical through an angle of a few degrees. a

Near the'lower end of the tube 34 are two brackets 45 each of which is provided with two holes 46 (FIG- URE/6). Fitted in these holes are pins which are surrounded by flexible bushes 47. Secured crosswise to the housings of the bushes 47 as by welding or brazing are housings of further flexible bushes 48 the pins of which are fixed in the ends of connecting rods 58. At the other ends of these connecting rods 59 are mounted the pins of flexible bushes 52. The housings of the bushes 52 are connected to bearing housing portions 53 which enclose shielded ball bearings which run on vertical bolts 54, the bolts 54 having heads on their lower ends which fit into T-section slots 55 formed diametrically in crank discs 56. The crank discs 56 are mounted on the upper ends of shafts 57 (see FIGURE 4) the lower ends of which are fitted with pulleys 53. A belt'59 passes round the pulleys 58 and round the pulley 18, the diflierence in diameter of the pulleys l7 and 18 constituting a speed reduction gearing. Although the pulleys 58 are .both of the same diameter, the fact that they are driven by a non-positive drive, ie by a friction belt, means that they do not at all times rotate, at identical speeds, owing to slight slip of the belt. The rotation of the pulleys 58 and the shafts 57 causes the crank discs 56 toarotate and the bolts 54 to describe circular paths, the radius of such. circular path depending upon the degree of eccentricity to which the respective pin 54 is adjusted in its slot 55 in relation to the centre of the respective disc 56. Thus, through the connecting rods 50 the lower end of the tube 34 is caused to perform irregular oscillatory movements, these movements being permitted by the flexibility of the bush in the tubular shaft 29. The slow circular motion of the rod 33 due to its eccentricity in relation to the tubular shaft 29 increases the irregularity of the movementsof the lower end of the tube 34, which irregularity is desirable for good grinding.

The flexible bushes referred to may be of rubber or other elastomeric material. Such bushes, which are conventional articles of commerce, permit limited angular movement of their. pins in relation to their housings without any relative sliding, and are eminently suitable for an abrasive environment.

Referringmore particularly to FIGURES and 6, at the bottom of the tube 34 is a cross-piece 61 with two vertical tubes 62 at its ends, the lower ends of which are fitted with nylon or other abrasion-resistant and downwardly-facing ball sockets 63. Beneath the crosspiece 61 is a yoke 64 having balls 65 at its ends which enter the sockets 63, permitting the yoke to rock, in relation to the tube 34 and the cross-piece 61, about an axis through the centres of the balls 65. Fixed transversely to the yoke '64 is a cross-piece 66 which has downwardly-projecting pins 67 near its ends. These pins 67 have hemispherical ends and fit into rounded sockets in the back of lens mounting disc 68 so that the disc can rock about an axis through the centres of the hemispherical ends of the pins 67. The lens 69 is detachably secured to the disc 63 in the conventional manner by wax or pitch 70. The lens can thus tilt about two axes which are at right angles but which, in this embodiment, do not intersect.

The lens is moved with irregular movements over the surface 71 of a tool 72, the shape of which surface is the complement of the desired surface of the lens 69. The abrasive medium is pumped to flood over the tool and lens through the rubber tube (not shown) which has been mentioned above. The tool is detachably mounted in a holder 73 (FIGURE 2) which is fixed to the base 10 by threaded shank 74. The lens 69 is pressed against the tool 72 by springs 75 attached to the cross-piece 35 and, at their lower ends, to a hinged frame 7 6, which frame has a downward force' applied to it by a pneumatic cylinder 77. V

Theoretically, both the axes about which the lens 69 can tilt should be tangential to the tool surface 71, and although this is possible for the axis through the centres of the balls 65 it is not possible in this embodiment, for the axis through the ends of the pins 67 which, being behind the lens 69, are necessarily above the surface being ground.

FIGURES 7 to 9 show an improved lens mountin means resembling a gimbal, in which the pivotal axes of the lens intersect at right angles and can be disposed tangentially to the tool surface. By these means, which are used in conjunction with the cross-piece 61, the vertical tubes 62 and the ball sockets 63 of FIGURES 5 and 6, the balls which enter the. sockets 63-are at diametrically opposite points of a light tubular ring 81, which ring is of shallow V form when viewed from one side as shown in FIGURE 7.. The balls 80 are at the base of the V. At 90 from the balls 89 are ball sockets 82. A yoke 84 extends diametrically across the ring 81, this yoke having balls 85 at its ends which enter the ball sockets 82'- Fixed to the centre of the yoke 84 is an inverted cup 86 lined at 87 with rubber or a somewhat flexible plastic material and having two downwardly-extending pins 88. The cup is intended to receive, as a detachable snug fit, a lens mounting disc (not shown) similar to the disc 68 in the first embodiment. The pins 83 enter sockets in the back of the disc and prevent the disc and lens from rotating. The axis through the centres of the balls 80 intersects at right angles the axis through the centres of the balls 85, and since all the balls are spaced radially outwards from the cup 86 the lens can be accommodated within the ring 81 with freedom to tilt in any direction and in such a position that when it is in contact with the tool the said axes are substantially tangential to the tool surface.

Although machines embodying the invention are primarily for grinding work-pieces such as cylindrical or toroidal lenses where rotation of the work-piece about an axis normal to the surface being ground must be prevented, the machines could be used for grinding workpieces such as spherical lenses where such rotation would not matter.

What I claim as my invention and desire to secure by Letters Patent is:

1. A grinding machine comprising a work-piece holder arm having a first end and a second end, work-piece mounting means on said first end of said arm, a support, universal bearing means on said support, means connecting said second end of said arm to said universal bearing means, linkage means connecting'said arm to said support to prevent rotation of said arm but permit limited swinging movements of said arm about said universal bearing means in all directions transverse to the length of said arm, driving means for producing said swinging movements of said arm, and a stationary tool adjacent said work-piece mounting means.

7 2. A grinding machine according to claim 1 in which said universal bearing means comprises a flexible bush.

3. A grinding machine according to claim 1 in which said linkage means comprises pivots constituted by flexible bushes.

4. A grinding machine according to claim 1 in" which said linkage means comprises laterally flexible link members.

5. A grinding machine according to claim 1 in which said driving means comprises two cranks, drive means to drive said cranks at diflerent speeds, two connecting rods, connection means connecting said connecting rods to said cranks and connection means connecting said connecting rods to said arm.

6. A grinding machine according to claim 5 in which said connection means comprise flexible bushes.

7. A grinding machine according to claim 1 in which said means connecting said second end of said arm to said universal bearing means includes an eccentric member, and in which said machine includes drive means to rotate said eccentric member and move said second end of said arm along a circular path.

8. A grinding machine according to claim 1 in which said mounting means for said work-piece comprises a gimbal ring, first pivot means on a first diametric axis of said gimbal ring, means connecting said first end of said arm to said first pivot means, second pivot means on a second diametric axis of said gimbal ring, said axes intersecting each other at right angles, yoke means mounted on said second pivot means and a Work-piece mounting on said yoke means.

9. A grinding machine comprising a base, a support on said base, a work-piece holder arm having an upper end and a lower end, a flexible bush on said support, means connecting said upper end of said arm to said flexible bush, linkage means connecting said arm to said support, said linkage means including flexible pivot bushes and laterally flexible link members to prevent rotation of said arm but permit limited horizontal swinging movements of said arm about said first-mentioned flexible bush, two cranks, drive means to drive said cranks at different speeds, two connecting rods, connection means connecting said connecting rods to said cranks, connection means connecting said connecting rods to said arm to produce said swinging movements thereof, work-piece mounting means on said lower end of said arm, and a stationary tool disposed adjacent said work-piece mounting means.

10. A grinding machine according to claim 9 also including driving means to rotate said first-mentioned flexible bush, an eccentric member mounted in said flexible bush to rotate therewith, and means connecting said upper end of said arm to said eccentric member eccentrically to the axis of rotation of said eccentric member.

11. Work-piece mounting means comprising a holder, 21 gimbal ring, first pivot means disposed on a first diametric axis of said gimbal ring, means connecting said first pivot means to said holder, second pivot means disposed on a second diametric axis of said gimbal ring, said axes intersecting each other at right angles, yoke means mounted on said second pivot means and a Work-piece mounting on said yoke means.

References Cited in the file of this patent UNITED STATES PATENTS 1,559,908 Parsons et al Nov. 3, 1925 2,141,309 McCabe et al Dec. 27, 1938 2,168,843 Lockhart Aug. 8, 1939 

1. A GRINDING MACHINE COMPRISING A WORK-PIECE HOLDER ARM HAVING A FIRST END AND A SECOND END, WORK-PIECE MOUNTING MEANS ON SAID FIRST END OF SAID ARM, A SUPPORT, UNIVERSAL BEARING MEANS ON SAID SUPPORT, MEANS CONNECTING SAID SECOND END OF SAID ARM TO SAID UNIVERSAL BEARING MEANS, LINKAGE MEANS CONNECTING SAID ARM TO SAID SUPPORT TO PREVENT ROTATION OF SAID ARM BUT PERMIT LIMITED SWINGING MOVEMENTS OF SAID ARM ABOUT SAID UNIVERSAL BEARING MEANS IN ALL DIRECTIONS TRANSVERSE TO THE LENGTH OF SAID ARM, DRIVING MEANS FOR PRODUCING SAID SWINGING MOVEMENTS OF SAID ARM, AND A STATIONARY TOOL ADJACENT SAID WORK-PIECE MOUNTING MEANS. 